Make TLS write functions' buffer arguments pointers const

This also makes it match the equivalent APIs in libpq.

Author: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
Discussion: https://www.postgresql.org/message-id/flat/fd1fcedb-3492-4fc8-9e3e-74b97f2db6c7%40eisentraut.org

src/backend/libpq/be-secure-gssapi.c

@@ -93,7 +93,7 @@ static uint32 PqGSSMaxPktSize;	/* Maximum size we can encrypt and fit the
  * failure if necessary, and then return an errno indicating connection loss.
  */
 ssize_t
-be_gssapi_write(Port *port, void *ptr, size_t len)
+be_gssapi_write(Port *port, const void *ptr, size_t len)
 {
 	OM_uint32	major,
 				minor;

src/backend/libpq/be-secure-openssl.c

@@ -821,7 +821,7 @@ be_tls_read(Port *port, void *ptr, size_t len, int *waitfor)
 }
 
 ssize_t
-be_tls_write(Port *port, void *ptr, size_t len, int *waitfor)
+be_tls_write(Port *port, const void *ptr, size_t len, int *waitfor)
 {
 	ssize_t		n;
 	int			err;

src/backend/libpq/be-secure.c

@@ -302,7 +302,7 @@ secure_raw_read(Port *port, void *ptr, size_t len)
  *	Write data to a secure connection.
  */
 ssize_t
-secure_write(Port *port, void *ptr, size_t len)
+secure_write(Port *port, const void *ptr, size_t len)
 {
 	ssize_t		n;
 	int			waitfor;

src/backend/libpq/pqcomm.c

@@ -1368,7 +1368,7 @@ internal_flush_buffer(const char *buf, size_t *start, size_t *end)
 	{
 		int			r;
 
-		r = secure_write(MyProcPort, (char *) bufptr, bufend - bufptr);
+		r = secure_write(MyProcPort, bufptr, bufend - bufptr);
 
 		if (r <= 0)
 		{

src/include/libpq/libpq-be.h

@@ -312,7 +312,7 @@ extern ssize_t be_tls_read(Port *port, void *ptr, size_t len, int *waitfor);
 /*
  * Write data to a secure connection.
  */
-extern ssize_t be_tls_write(Port *port, void *ptr, size_t len, int *waitfor);
+extern ssize_t be_tls_write(Port *port, const void *ptr, size_t len, int *waitfor);
 
 /*
  * Return information about the SSL connection.
@@ -352,7 +352,7 @@ extern bool be_gssapi_get_delegation(Port *port);
 
 /* Read and write to a GSSAPI-encrypted connection. */
 extern ssize_t be_gssapi_read(Port *port, void *ptr, size_t len);
-extern ssize_t be_gssapi_write(Port *port, void *ptr, size_t len);
+extern ssize_t be_gssapi_write(Port *port, const void *ptr, size_t len);
 #endif							/* ENABLE_GSS */
 
 extern PGDLLIMPORT ProtocolVersion FrontendProtocol;

src/include/libpq/libpq.h

@@ -92,7 +92,7 @@ extern void secure_destroy(void);
 extern int	secure_open_server(Port *port);
 extern void secure_close(Port *port);
 extern ssize_t secure_read(Port *port, void *ptr, size_t len);
-extern ssize_t secure_write(Port *port, void *ptr, size_t len);
+extern ssize_t secure_write(Port *port, const void *ptr, size_t len);
 extern ssize_t secure_raw_read(Port *port, void *ptr, size_t len);
 extern ssize_t secure_raw_write(Port *port, const void *ptr, size_t len);